This study will measure subjectively & objectively subjects' reations to ingestion of D20 at 0.25% and 0.5% enrichment. Specifically, the dose-response effect on the VOR will be measured over an 8 hour period in 10 healthy subjects. Deuterated water is increasingly being used in metabolic research to quantify the contribution of gluconeogenesis to total endogenous glucose production. However, little is known about the effect of D20 enrichment of body water on the vestibulo-ocular reflex & equilibrium effects.